diff --git a/libraries/AP_Scripting/generator/src/main.c b/libraries/AP_Scripting/generator/src/main.c
index 7f2257465b..79e022b3d3 100644
--- a/libraries/AP_Scripting/generator/src/main.c
+++ b/libraries/AP_Scripting/generator/src/main.c
@@ -32,6 +32,8 @@ char keyword_global[]              = "global";
 char keyword_creation[]            = "creation";
 char keyword_manual_operator[]     = "manual_operator";
 char keyword_operator_getter[]     = "operator_getter";
+char keyword_field_valid_mask[]    = "valid_mask";
+
 
 // attributes (should include the leading ' )
 char keyword_attr_enum[]    = "'enum";
@@ -184,6 +186,10 @@ struct type {
     char *enum_name;
     char *literal;
   } data;
+  struct {
+    char *name;
+    char *value;
+  } valid_mask;
 };
 
 int TRACE_LEVEL = 0;
@@ -510,6 +516,12 @@ unsigned int parse_access_flags(struct type * type) {
             error(ERROR_INTERNAL, "Can't access a NONE type");
         }
       }
+    } else if (strcmp(state.token, keyword_field_valid_mask) == 0) {
+      char * name = next_token();
+      string_copy(&(type->valid_mask.name), name);
+      char * value = next_token();
+      string_copy(&(type->valid_mask.value), value);
+
     } else {
       error(ERROR_UNKNOWN_KEYWORD, "Unknown access provided: %s", state.token);
       break;
@@ -1716,10 +1728,20 @@ void emit_field(const struct userdata_field *field, const char* object_name, con
     fprintf(source, "    binding_argcheck(L, %d);\n",args);
   }
 
+  int valid_mask = (field->type.valid_mask.name != NULL) & (field->type.valid_mask.value != NULL);
+
   if (field->access_flags & ACCESS_FLAG_READ) {
     if (use_switch) {
       fprintf(source, "        case 1:\n");
     }
+
+    // Check if field is valid
+    if (valid_mask) {
+        fprintf(source, "%sif ((%s%s%s & %s) == 0) {\n", indent, object_name, object_access, field->type.valid_mask.name, field->type.valid_mask.value);
+        fprintf(source, "%s    return 0;\n", indent);
+        fprintf(source, "%s}\n", indent);
+    }
+
     switch (field->type.type) {
       case TYPE_BOOLEAN:
         fprintf(source, "%slua_pushinteger(L, %s%s%s%s);\n", indent, object_name, object_access, field->name, index_string);
@@ -1764,6 +1786,12 @@ void emit_field(const struct userdata_field *field, const char* object_name, con
       fprintf(source, "        case 2: {\n");
     }
     emit_checker(field->type, write_arg_number, 0, indent);
+
+    // set field valid
+    if (valid_mask) {
+      fprintf(source, "%s%s%s%s &= %s;\n", indent, object_name, object_access, field->type.valid_mask.name, field->type.valid_mask.value);
+    }
+
     fprintf(source, "%s%s%s%s%s = data_%i;\n", indent, object_name, object_access, field->name, index_string, write_arg_number);
     fprintf(source, "%sreturn 0;\n", indent);
     if (use_switch) {
@@ -2927,11 +2955,14 @@ void emit_docs(struct userdata *node, int is_userdata, int emit_creation) {
     if (node->fields != NULL) {
       struct userdata_field *field = node->fields;
       while(field) {
+          int valid_mask = (field->type.valid_mask.name != NULL) & (field->type.valid_mask.value != NULL);
+          const char * return_postfix = valid_mask ? "|nil\n" : "*\n";
+
           if (field->array_len == NULL) {
             // single value field
             if (field->access_flags & ACCESS_FLAG_READ) {
               fprintf(docs, "-- get field\n");
-              emit_docs_type(field->type, "---@return", "\n");
+              emit_docs_type(field->type, "---@return", return_postfix);
               fprintf(docs, "function %s:%s() end\n\n", name, field->rename ? field->rename : field->name);
             }
             if (field->access_flags & ACCESS_FLAG_WRITE) {
@@ -2944,7 +2975,7 @@ void emit_docs(struct userdata *node, int is_userdata, int emit_creation) {
             if (field->access_flags & ACCESS_FLAG_READ) {
               fprintf(docs, "-- get array field\n");
               fprintf(docs, "---@param index integer\n");
-              emit_docs_type(field->type, "---@return", "\n");
+              emit_docs_type(field->type, "---@return", return_postfix);
               fprintf(docs, "function %s:%s(index) end\n\n", name, field->rename ? field->rename : field->name);
             }
             if (field->access_flags & ACCESS_FLAG_WRITE) {